Select all the correct answers. This graph gives information on greenhouse gas (GHG) emissions from generating electricity in the United States. Which questions would help clarify this evidence? Why does producing electricity cause greenhouse gas emissions? Why do power plants release hydrofluorocarbons and other F-gases? Why did greenhouse gas emissions decrease between 2007 and 2009? Are greenhouse gases released because of food digestion in cattle? Where is the data on greenhouse gas emissions from volcanic eruptions?.